The present invention generally relates to systems for monitoring and/or affecting parameters of a patient's body for the purpose of medical diagnosis and/or treatment. More particularly, such systems are characterized by a plurality of devices, preferably battery powered, configured for implanting within a patient's body, each device being configured to sense a body parameter, e.g., temperature, O2 content, physical position, electrical potential, etc., and/or to affect a parameter, e.g., via nerve and/or muscle stimulation.
Commonly owned U.S. Pat. No. 6,164,284 entitled “System of Implantable Devices For Monitoring and/or Affecting Body Parameters” and U.S. Pat. No. 6,185,452 entitled “Battery Powered Patient Implantable Device”, each incorporated herein by reference in their entirety, describe devices configured for implantation within a patient's body, i.e., beneath a patient's skin, for performing various functions including: (1) stimulation of body tissue and/or sensing of body parameters, and (2) communicating between implanted devices and devices external to a patient's body. Depending upon the ailment affecting the patient, it may be desirable to communicate with a number of different devices, e.g., from one to thousands, while maintaining an update rate, e.g., on the order of every 1 millisecond to every second, sufficient to control and/or monitor the body parameter(s) at issue. Commonly owned U.S. Pat. No. 6,472,991 entitled “Multichannel Communication Protocol Configured To Extend The Battery Life Of An Implantable Device”, incorporated herein by reference in its entirety, describes an exemplary communication protocol for communicating between a master device (referred to as a system control unit (SCU) in the referenced patent) which may be implanted or in proximity to a patient that communicates with a plurality of slave devices, preferably implantable, across a common communication channel during a frame period, preferably of fixed duration. The frame periods are essentially sequential and temporally contiguous and as such there is only one repeatable frame period available that occupies the entire temporal bandwidth of the common communication channel. Fortunately, while this exemplary communication protocol allocates time slots for a large number of implantable slave devices, most systems will not be populated to that predefined maximum amount. This allows for a gap within the frame period that is specified relating to the actual number of implantable slave devices in the system or the system configuration. Unfortunately, when multiple systems of devices, i.e., a master device and associated slave devices, are in close proximity, i.e., within an interference communication range of each other, interference between the master or slave devices in different systems may cause one or more devices or systems to perform improperly since there is a statistical probability that two or more devices may transmit during the same or overlapping time slots and consequently result in difficulty in receiving by individual receivers. Accordingly, the present invention is directed to a system and method that facilitate multiple systems to coexist on a common communication channel while maintaining the required update rate.